A radar device detects a target related to an object by receiving a reception signal obtained when a transmission signal transmitted from the radar device is reflected by the object (for example, see Japanese Laid-open Patent Publication No. 2016-006383).
Examples of the radar device include a millimetric wave radar. The radar device is, for example, mounted on a vehicle, and detects a target related to an object that is present in the periphery of the vehicle by using a frequency modulated continuous wave (FM-CW).
The object to be detected by the radar device mounted on the vehicle is, for example, divided broadly into a stationary object and a moving object. Examples of the stationary object include a traffic light, a pole, a pedestrian bridge, a utility pole, a traffic sign, a guardrail, and a road guide plate placed on a road surface, a side strip, a footpath, and the like. Examples of the moving object include another vehicle (hereinafter, also referred to as “leading vehicle” in some cases) traveling in front of an own vehicle toward the same direction as the own vehicle.
The radar device mounted on the vehicle calculates “reliability” of the target as data related to classification of each target. Examples of the target having relatively low reliability include a target related to a stationary object (hereinafter, also referred to as “upper object” in some cases) placed at a position that is higher, by a predetermined distance, than a height of the vehicle on which the radar device is mounted, and a target related to a stationary object (hereinafter, also referred to as “lower object” in some cases) placed at a position lower than the bottom of the vehicle on which the radar device is mounted. Examples of the upper object include a pedestrian bridge and a road guide plate, and examples of the lower object include a road rivet arranged at a median strip or a curve of a road. Examples of the target having relatively high reliability include a target related to a vehicle (hereinafter, also referred to as “standing vehicle” in some cases) being stopped in its own lane, and a target related to a leading vehicle. The radar device outputs information about a target having reliability equal to or larger than a threshold to a vehicle control device that controls behavior of the vehicle, and does not output information about a target having reliability smaller than a threshold to the vehicle control device.
When the radar device detects a target related to a standing vehicle the total length of which is relatively long (for example, a truck), a transmission wave may be reflected at a plurality of points on the standing vehicle. In this case, a plurality of reflected waves arrives at the radar device from one standing vehicle. For example, a reception signal R1 is received by the radar device when the transmission wave is reflected at a position of a rear bumper arranged at a rear end of the standing vehicle, and a reception signal R2 is received by the radar device when the transmission wave is reflected at a position of a side mirror arranged in the vicinity of a driver's seat at the front part of the truck. When the reception signal R1 and the reception signal R2 are received from one standing vehicle, the radar device detects two targets, that is, a target P1 related to a reflection point of the rear bumper and a target P2 related to a reflection point of the side mirror. A case in which a plurality of targets is detected for one object as described above may be referred to as a “longitudinal multi-identification”. Hereinafter, an object for which the longitudinal multi-identification is caused may be referred to as a “longitudinal multi-identification object”.
On the other hand, a vehicle control device often uses a target related to the rear end (for example, the rear bumper) of the standing vehicle as a reference point for vehicle control. For example, an advanced emergency braking system (AEBS) serving as a vehicle control device causes a brake of the own vehicle to operate to prevent collision with the standing vehicle when a distance between the own vehicle and the rear end of the standing vehicle becomes smaller than a threshold.
However, the reflected waves from the standing vehicle include not only a direct wave that is directly received from the reflection point by the radar device but also a multipath wave that is indirectly received from the reflection point by the radar device after being reflected by the ground. In some cases, the multipath wave from a portion other than the rear end of the standing vehicle interferes with the direct wave from the rear bumper, and the target P1 is unable to be detected because power of the reception signal R1 is lowered.
When the target P2 is detected while power of the reception signal R2 is not interfered with by the multipath wave, the radar device detects the target P2 related to the side mirror earlier than the target P1 related to the rear bumper of the standing vehicle. As a result, the position of the target P2 is detected as the position of the standing vehicle, and determination processing of classification of the target P1 is delayed, the target P1 being used as the reference point of the vehicle control device. When the determination processing of classification of the target is delayed in the radar device as described above, processing of determining whether a target of interest is a target that needs vehicle control is delayed in the vehicle control device. As a result, if the target of interest is the target that needs vehicle control, vehicle control (for example, start of braking of the vehicle by the AEBS) is delayed.